1. Field of the Invention
The present invention relates to an axle driving unit suitable for use with a rear-discharge lawn tractor having a mower located beneath the body of the tractor between the front and rear wheels.
2. Related Art
U.S. Pat. No. 3,969,876 discloses a conventional lawn tractor having a rear discharge system, which has a mower driven by a prime mover mounted on it, and a leaf blower loaded on the rear portion of the tractor. The rear discharge system disposes a chute, for discharging lawn grass cut by the mower, longitudinally between the left and right rear wheels. The rear discharge system has no projection to the outside of the body of the tractor. The cut lawn grass is discharged directly rearwardly of the tractor. This has the advantage of eliminating equipment, such as an auxiliary suction fan.
However, because the space between the left and right rear wheels is very narrow, it is very difficult to laterally juxtapose therebetween the cut grass chute and an axle driving apparatus. As disclosed in U.S. Pat. No. 3,969,876, a hydraulic stepless speed change transmission and a differential gear constituting the axle driving unit are separated and are housed in separate housings. The differential gear is disposed in the narrow space between the wheels, and the transmission is disposed at another position on the body of the tractor. The output shaft of the hydraulic stepless speed change transmission and differential gear are connected by a chain belt mechanism. Accordingly, the axle driving unit has the disadvantages of a high manufacturing cost and a long assembly time. Also, since one axle, through which the cut grass chute passes, is much longer than the other axle, this design has the further disadvantage that the one longer axle is easy to deflect. Accordingly, the life span of a bearing for the one longer axle provided at the differential gear is reduced.
An axle driving unit which houses in a common housing a hydraulic stepless speed change transmission and a differential gear for differentially connecting a pair of axles and integrates them is well-known, as disclosed in, for example, U.S. Pat. No. 4,914,907 and U.S. Pat. No. 4,932,209. In these patents, the transmission comprises a combination of a variable displacement type hydraulic pump and a fixed displacement hydraulic motor. The hydraulic pump and motor are mounted side by side and longitudinally of the axle with respect to an L-like-shaped center section, whereby the entire axle driving unit is larger in width longitudinally of the axle. Hence, the axle driving unit of this design interferes with the chute of a lawn tractor which has a rear discharge system. As a result, the chute cannot be disposed between the left and right rear wheels.